#4 He's been primarily a face in NXT and on the main roster so far
Black's entire run in NXT was as a face. He took on all comers from Lars Sullivan to Velveteen Dream to Johnny Gargano. And when he and Ricochet debuted on the main roster a few months ago, they did so as faces.
A decent amount of superstars from NXT debut on the main roster as the opposite of what they were in NXT. Bobby Roode was a brilliant heel in NXT but was a face up until this week. Drew McIntyre was a face during his time in NXT. Ruby Riott was bullied in NXT but joined the main roster as the leader of a trio of ladies who sought to cause chaos.
With all of that time spent as a face for Black, it's certainly a good choice to explore what he can do as a heel. He has plenty of backstory due to his tattoos and persona, but those two facets of the man have barely been explored.